Defect Sizing in Pipeline Welds: What Can We Really Achieve?

Pipelines are now using Fitness-For-Service (FFS) for accept/reject of weld defects. FFS requires accurate measurement of defect height for Fracture Mechanics assessments. The standard pipeline weld inspection technique of radiography is incapable of such measurements. However, the newer technique of ultrasonics can measure defect height, in principle. Initially ultrasonic amplitude methods were used for height measurement, but these proved unreliable. Now diffraction methods, especially Time-Of-Flight-Diffraction (TOFD), are being used in conjunction. This paper reviews previous work — mainly large nuclear studies like PISC II — and published pipeline sizing studies. The best nuclear sizing was within a few millimetres, using diffraction. In contrast to nuclear, pipeline AUT uses zone discrimination, focused transducers, much thinner material and simpler analysis techniques. Current accuracies are typically ± 1 mm (terminology undefined), which correlates with the beam spot size and typical weld pass. Requests for accuracies of ± 0.3 mm are probably unachievable, though future R&D should significantly improve pipeline sizing.

Time Frequency Domain Analysis of the Dispersion of Guided Wave Modes

One of unique characteristics of guided waves is a dispersive behavior that guided wave velocity changes with an excitation frequency and mode. In practical applications of guided wave techniques, it is very important to identify propagating modes in a time-domain waveform for determination of defect location and size. Mode identification can be done by measurement of group velocity in a time-domain waveform. Thus, it is preferred to generate a single or less dispersive mode. But, in many cases, it is difficult to distinguish a mode clearly in a time-domain waveform because of superposition of multi modes and mode conversion phenomena. Time-frequency analysis is used as efficient methods to identify modes by presenting wave energy distribution in a time-frequency. In this study, experimental guided wave mode identification is carried out in a steel plate using time-frequency analysis methods such as wavelet transform. The results are compared with theoretically calculated group velocity dispersion curves. The results are in good agreement with analytical predictions and show the effectiveness of using the wavelet transform method to identify and measure the amplitudes of individual guided wave modes.

Crack Sizing of Deep Cracks in Eddy Current Testing Using 3D Electromagnetic Field Analysis

A computer-aided approach of the eddy current testing (ECT) is described to detect and to size up deep cracks in thick metal structures. A 3D eddy current field analysis based on the finite elements performs designing ECT probes and evaluating the size of crack depth quantitatively. An exhaustive study on the ECT probe specification gives the optimal design of coil elements and their combination. The experimental verification shows that the developed ECT probe employing double exciting coils is capable of detecting crack depth over 10mm from the inspection surfaces. The depth of cracks is quantitatively evaluated from the measured ECT signals with the help of numerical calculation. The results of evaluation profile the crack shapes with fairly high accuracy, supporting our approach.

Detection of Corrosion of Insulated Piping Using SH Angle Probe

One of the serious problems regarding insulated piping in petroleum and petrochemical plants is external surface corrosion. In general, visual inspection after removing insulation is carried out to detect corrosion. However, removing insulation is uneconomical, namely high cost, and time consuming processes are necessary such as setting up a scaffold. Ultrasonic guided wave technique has potential possibility to detect corrosion of long piping and has been recently investigated regarding its propagation characteristics. In this study, guided wave generated by horizontally polarized shear (SH) wave is applied to detect corrosion of insulated piping ranging from 1B to 3B. The reason why we select SH wave is that it has an advantage of being insensitive to internal fluid in piping. Through this study it is clear that SH guided wave is applicable to small diameter piping because sound beam of SH wave propagates along the longitudinal direction without circumferential extent. Accordingly local corrosion can be detected using SH guided wave technique.

Flaw Classification by Using Artificial Neural Network and Wavelet

This paper presents a methodology to 2-D flaw-shape recognition by combining a neural network and the wavelet feature extractor. This approach consists of three stages. First, the 2-D pattern of an object is retrieved from image and then transformed to complex contour, which is described by the coordinates of its shape. Then, feature extraction is performed to this contour representation. Fourier descriptor (FD), principal component analysis (PCA) and wavelet descriptor (WD) are employed in this stage, and their performances are compared and discussed. In the third stage, artificial neural networks, including two different types of multi-layer perceptron (MLP) and Kohonen self-organizing network, are used as the classifier based on the feature sets extracted in the second stage. The numerical experiments performed on the recognition of simulated shapes demonstrate the superiority of the WD feature extractor (both used for MLP and Kohonen network classifiers) to the other two: PCA and FD, especially when the raw data have poor signal-to-noise ratio (SNR). The application to the real ultrasonic C-scan image flaw-shape classification shows the effectiveness of the proposed approach to the field of PVP.

Degradation Estimation of 2.25CR-1Mo Steel by Barkhausen Noise Method

In this study, various NDE parameters of the Barkhausen noise method, such as MPA (Maximum Peak Amplitude), RMS, IABNS (Internal Area of Barkhausen Noise on Signal) and average amplitude of frequency spectrum are investigated and correlated with thermal damage level of 2.25Cr-1.0Mo steel using wavelet analysis. Those parameters tend to increase while thermal degradation proceeds. It also turns out that the wavelet technique can help to reduce experimental false calls in data analysis.

Fatigue Damage Evaluation in CFRP Woven Fabric Composites Through Dynamic Modulus Measurements

Advanced fiber reinforced composite materials offer substantial advantages over metallic materials for the structural applications subjected to fatigue loading. With the increasing use of these composites, it is required to understand their mechanical response to cyclic loading [1–4]. Our major concern in this work is to macroscopically evaluate the damage development in composites during fatigue loading. For this purpose, we examine what effect the fatigue damage may have on the material properties and how they can be related mathematically to each other. In general, as the damage initiates in composite materials and grows during cyclic loading, material properties such as modulus, residual strength and strain would vary and, in many cases, they may be significantly reduced because of the progressive accumulation of cracks. Therefore, the damage can be characterized by the change in material properties, which is expected to be available for non-destructive evaluation of the fatigue damage development in composites. Here, the tensiontension fatigue tests are firstly conducted on the plain woven fabric carbon fiber composites for different loading levels. In the fatigue tests, the dynamic elastic moduli are measured on real-time, which will decrease with an increasing number of cycles due to the degradation of stiffness. Then, the damage fimction presenting the damage development during fatigue loading is determined from the dynamic elastic moduli thus obtained, from which the damage function is formulated in terms of a number of cycles and an applied loading level. Finally, the damage function is shown to be applied for predicting the remaining fifetime of the CFRP composites subjected to two-stress level fatigue loading.

Effect of Sputtering Gas Pressure and Bias Voltage on Mechanical Properties of TiN Coating Deposited by DC Magnetron Sputtering

The mechanical properties of TiN films deposited on carbon steel JIS S45C by reactive dc magnetron sputtering under three sputtering gas pressures, 0.5Pa, 0.8Pa, and 1.76Pa were investigated. The residual stress once increased and then decreased with increasing bias voltage at 0.5Pa and 0.8Pa, but increased monotonously at 1.76Pa. These variations could be explained by the variations of the bombarding energy of a sputtered ion at each gas pressure. The variations of hardness and toughness correlated with the variation of residual stress. The variation of adhesive strength also could be explained by the variation of the bombarding energy with a model proposed in this study. A specific wear rate was also investigated, and it was found that to increase not only the hardness but also the adhesive strength is necessary to improve the wear resistance of TiN films.

A Novel Method of Estimating the Aspect Ratio of Pipe Wall Thickness to Diameter Utilizing the Characteristics of a Hollow Cylindrical Guided Wave

We have developed a method of estimating the aspect ratio of a pipe wall thickness to diameter (t/d) using a hollow cylindrical guided wave (HCGW). The HCGW is an ultrasonic guided wave in a pipe. The method is very useful for onsite and nondestructive estimation of pipe wall thickness. It is based on the change of the dispersion relation of the HCGW as a function of t/d. The group velocity of the primary wave (first arriving wave packet from an impulse source) of the HCGW ranges from the bar velocity to the sheet velocity as a function of t/d. The bar velocity is the velocity of the DC component of the guided wave propagating in a solid cylinder; the sheet velocity is that of the S0 mode Lamb wave. The first part of the paper describes the principle of the method. In the last part, a laser ultrasonic method was employed to verify the method in both time- and time-frequency domains. The experimental results for aluminum pipes with various t/d’s were in good agreement with the theory.

An Investigation on Monitoring Methods of Creep Damage Using Ultrasonic Technique

The reliability of facilities under long-term operation, that is to prevent trouble or accident, is one of the most important matters in the field of petroleum and petrochemical plants. For this purpose, some kinds of non-destructive inspection methods are carried out periodically to detect damages or degradation of material. Moreover, to enrich the reliability of safety operation of the plants, continuous monitoring methods to detect material degradation without mistiming are required. Recently, ultrasonic method has been developed as a key technology to detect and evaluate the damage of materials. One of the advantages of ultrasonic technique is to obtain much information about microstructure change due to material degradation when ultrasounds travel through the material. Further, ultrasonic technique has also the potential ability to be applied for continuous monitoring methods. The objective of this study is to accomplish monitoring methods of creep damage using ultrasonic technique. A novel technique to acquire the ultrasonic data during uni-axial creep test is investigated as the first step of monitoring of creep damage. As a result, it is confirmed that the sound velocity in time domain decreases gradually in creep acceleration stage which starts at the creep life fraction of 0.6 and the gravity frequency in frequency domain begins to increase at the creep life fraction of 0.8. Therefore, the possibility to monitor the creep damage under continuous operation by ultrasonic technique is suggested.